WEDNESDAY, Feb. 6 (HealthDay News) -- The number of Americans afflicted with Alzheimer's disease could triple within the next 40 years if no progress is made against the disease, new projections show.

Reporting in the Feb. 6 online issue of the journal Neurology, researchers say that by 2050, nearly 14 million Americans could have Alzheimer's -- the most common form of dementia. That's close to triple the prevalence in 2010, when an estimated 4.7 million U.S. adults had the memory-robbing disease.

The new prediction is an update of a report published a decade ago -- which also projected a near-tripling in Alzheimer's disease in the next few decades.

So, not much has changed. "This is where we're headed if we don't make any progress in Alzheimer's research," said researcher Jennifer Weuve, an assistant professor at the Rush Institute for Healthy Aging in Chicago.

Unfortunately, she added, research into treating and delaying the disease has so far been "frustrating."

There are several drugs approved in the United States for slowing memory loss and other Alzheimer's symptoms -- brands like Aricept and Namenda. The medications work by affecting chemical messengers in the brain. But for many people, they either do not help or only work for a limited time.

Then there are the experimental "anti-amyloid" drugs, which target a protein that builds up and forms so-called plaques in the brains of people with Alzheimer's. But in studies so far, the medications have failed to help when given to people who already have moderate dementia symptoms.

Now, the hope is that they might work if given earlier in the game.

Research in the next several years could be pivotal, said Dr. P. Murali Doraiswamy, a psychiatry professor at Duke University Medical Center and an author of the book "The Alzheimer's Action Plan."

Three major clinical trials are starting this year, all looking at prevention in some way, Doraiswamy said. Two are testing drug treatment for people with gene mutations that cause inherited, early-onset Alzheimer's; the other involves older adults who have no dementia symptoms but do have amyloid deposits in their brains.

All of those studies are looking at anti-amyloid drugs.

Doraiswamy said that the risk is that researchers are "putting all their eggs in one basket" by focusing on amyloid-clearing drugs. The theory is that amyloid plaques are the root cause of dementia symptoms in Alzheimer's, but that's not a certainty.

Some other, smaller studies are testing other approaches, though, Doraiswamy said. One such trial is looking at whether supervised exercise can ward off or delay dementia in older adults with mild cognitive [mental] impairment -- less serious problems with memory and thinking that can eventually progress to Alzheimer's.

"If some of these trials succeed, we may be able to make a significant difference in the future prevalence of Alzheimer's," Doraiswamy said. "If they don't, we'll be back to the drawing board."

The latest findings are based on a long-term study of 10,800 older adults from Chicago who were evaluated for dementia; over 13 years, 402 were diagnosed with Alzheimer's. Weuve's team used U.S. Census data to extrapolate the findings to the whole population.

They estimate that, barring major research advances, 13.8 million Americans will have Alzheimer's in 2050 -- including 7 million people aged 85 or older.

It's thought that the brain damage in Alzheimer's begins a decade or more before symptoms emerge. There's also some evidence that the same risk factors for heart disease -- such as high blood pressure and diabetes -- might also be linked to Alzheimer's risk.

So, prevention may need to start early. "If we're going to make progress, we will probably have to focus on mid-life," Weuve said.

No one is sure, however, what the average person can do to prevent or delay Alzheimer's disease. A number of studies have linked certain lifestyle habits -- regular exercise, a healthy diet and staying mentally active -- to a lowered Alzheimer's risk. But it's not clear that those habits are the reason for the reduced risk.

"Right now, there is no magic bullet," Doraiswamy said. "But I would still encourage people to get regular exercise, to not smoke, to follow a healthy diet, like the Mediterranean diet." That diet is rich in fish, vegetables and fruit, whole grains and olive oil -- a source of "good" unsaturated fat.

According to the Alzheimer's Association, the United States spent about $200 billion in direct treatment costs for Alzheimer's and other forms of dementia in 2012. If no progress is made, that figure will top $1 trillion in 2050.

The good news is that there is now a national focus on Alzheimer's, said Maria Carrillo, vice president of medical and scientific relations for the Alzheimer's Association.

Last year, the Obama administration announced the creation of the National Plan to Address Alzheimer's Disease, which included funds for research, health care provider training and family caregiver support. It set a goal of finding effective treatment and prevention approaches by 2025.

"We're very hopeful," Carrillo said. But, she added, there needs to be continued "pressure" on government so that Alzheimer's is not forgotten. "This is an under-addressed crisis in the U.S.," she noted.

To help advance research, people with Alzheimer's and their families could also consider participating in clinical trials, Carrillo noted. "Many people don't even know that there are clinical trials, and that they're recruiting," she said.